Conventionally, in a lock mechanism for a seat track slide device, a lock lever accommodated in an upper rail is pivotally supported in the upper rail by a support shaft, a proximal end of a handle inserted into the upper rail from a front end thereof and a front end of a lock lever are joined to each other in the upper rail by an interlock support portion, so that the lock lever is interlocked with the handle and can be engaged with and disengaged from a lock recess in the lower rail as described in Patent Document 1, which will be discussed below. In this conventional lock mechanism, a lock lever is pivotally supported relative to an upper rail by a support shaft held between side plates of the upper rail. Therefore, assembly of the upper rail and the lock lever involves tedious work.
Under such circumstances, a lock lever is inserted into an upper rail and pivotally supported relative to the upper rail by a pivot support portion formed by inserting a protrusion into a recess in the upper rail in devices described in Patent Documents 2 and 3, which are discussed below, for example. Also, stoppers are provided that maintain the recess and the protrusion of the pivot support portion in an inserted state. Specifically, this upper rail has a pair of side plates, which are arranged side by side in a direction intersecting with a moving direction of the upper rail with an interval formed in between, and a top plate connecting the two side plates to each other. The lock lever has a pair of arm plate portions, which run in a direction intersecting with the moving direction of the upper rail with an interval formed in between. Of the recess and the protrusion of the pivot support portion, the recess is provided in the side plates of the upper rail, and the protrusions are provided on the arm plate portions of the lock member. In the top plate of the upper rail, a second stopper is placed between first stoppers provided in the two arm plate portions of the lock lever. Owing to engagement with the first and second stoppers, it is possible to prevent the protrusions and the recess from being separated from each other in a direction opposite to a direction in which the protrusions and the recesses of the pivot support portion are fitted by insertion, and it is possible to maintain the protrusions and the recesses of the pivot support portion in the inserted state.